From what I can see it's an ad service that the devloper of your sound app has included. The anoying add you are seeing is probably a failed/faulty ad from that provider. A template, rather than a finished ad at my guess.
Apparently Vungle ads are well known for being full screen, and difficult to dismiss. In my experience they usually have a faint X in one of the corners outside of where you think the actual advertisement covers. The actual ad is semi-transparent and tends to look like the main screen has just dimmed, rather than been covered up.
Some Possible Solutions:
1) You can try various ad blocking apps/services. These are somwhat effecive when browsing the internet, but less likely to work on ads presented by an app.
2) See if your app offers an ad free version, and pay the fee if you think it is worth it.
3) Switch apps.
4) Complain to the developer and hope they at least fix the faulty ad, if not remove all of them.
5) Live with it.
Note:
There was an earlier article, about a year old, that suggested these ads/apps could be fixed by restarting your iPad. Had something to do with Microsoft fixing or blocking the issue. Might be worth a try.
discussions.apple.com